Peripheral component interconnect express (PCI-E) is a standard for incorporating peripheral devices in computing systems and other electronic apparatuses. The standard defines interfaces and protocols for communication with PCI-E compatible devices and is commonly used in consumer and industrial applications as a motherboard level interconnect, a backplane interconnect, and an expansion card interface.
PCI-E has also been adapted for various modular applications, such as external chassis used to connect numerous peripheral devices to a host system. These modular applications have achieved popularity because they provide system integrators with flexibility to connect various peripheral devices according to their specific needs.
In an effort to standardize certain aspects of modular PCI-E applications, committees have developed compact PCI express (cPCI-E), which is a ruggedized version of PCI-E that can be used to incorporate peripherals in an external chassis, and PCI-E eXtensions for instrumentation (PXI-E), which is a version of cPCI-E adapted for test and measurement equipment such as oscilloscopes, logic analyzers, and so on.
A cPCI-E or PXI-E chassis typically comprises a system slot configured to receive a system control module, a plurality of peripheral slots each configured to receive a peripheral module, and a PCI-E switch fabric connected between the system slot and the peripheral slots. The chassis can be implemented in a standalone configuration where the system control module comprises an embedded controller such as a personal computer (PC) chipset, or it can be implemented in a hosted configuration where the system control module is connected to a remote host via a PCI-E cabled interface. A cPCI-E or PXI-E chassis can also be expanded through the use of cabled PCI-E modules, which can be inserted into the slots of the chassis and connected to additional downstream chassis or modules. For example, a cabled PCI-E module can be used to connect a first chassis to a second downstream chassis in a daisy chained configuration.
FIG. 1 is a diagram illustrating an example of a PXI-E chassis. As illustrated in FIG. 1, a PXI-E chassis 100 comprises a physical support structure 115, a plurality of module slots 1 through 18 configured to receive various PCI-E compatible modules, a cavity 105 configured to house and cool an embedded controller, and a backplane 110 located at the back of cavity 105 and behind module slots 1 through 18. Among module slots 1 through 18, slot 1 is a system slot, slot 10 is a timing slot, and slots 2 through 18 are peripheral slots.
System slot 1 is designated to receive a system control module for controlling modules in each of the other slots. In general, the system control module can be an embedded controller or a cabled PCI-E interface module, such as a cabled target module or host module. In several embodiments described below, it is assumed that system slot 1 is occupied by a cabled target module connected to a remote host such as a PC. System slot 1 comprises a connector for power, another two connectors for PCI-E, and an instrument specific connector.
Timing slot 10 is designated to receive a timing module for generating timing and synchronization signals for the other slots. It comprises a connector for providing timing signals as well as connectivity as a PXI-E peripheral slot. The remaining slots are designated to receive peripheral modules or cabled PCI-E interface modules, such as host modules or target modules. Peripheral slots 2-9 and 11-18 are all hybrid slots, with each one comprising a 32-bit PCI connector, a PCI-E connector, and a connector for instrument functions such as triggers and clocks. Timing slot 10 has special connectors dedicated to timing and synchronization functionality but can operate as a peripheral slot whether these resources are used or not.
The use of hybrid peripheral slots allows a user to insert either a PXI or a PXI-E module. A chassis that provides hybrid slots on all peripheral slots provides great flexibility for users to support a wide array of legacy PXI products available while providing the necessary upgrade path to higher performance PXI-E modules utilizing the latest PCI-E fabric technology.
Backplane 110, which typically comprises a printed circuit board (PCB), provides physical and logical support for module slots 1 through 18. For instance, as illustrated in FIG. 2, module slot 2 (and other module slots) can be physically mounted on backplane 110 bypress fitting associated slot connectors 210 into plated through hole vias (THVs) 205. Modules connected to module slots 1 through 18 can communicate with each other through a switch fabric, which is typically disposed on backplane 110, although it may alternatively be located, at least in part, on a mezzanine card connected to backplane 110.
Cavity 105 is located to the left of system slot 1 and has a size designed to accommodate an embedded controller connected to system slot 1. For instance, cavity 105 typically has a width large enough to accommodate a two-slot wide or four-slot wide embedded controller. In addition, cavity 105 typically has cooling facilities, such as a vertical airflow, configured to provide supplemental cooling for the embedded controller. For instance, cavity 105 may provide enough cooling for an embedded controller generating up to 140 watts of heat.
In general, a large number of electrical connectors may be required to support operations of PXI-E chassis 100. For instance, the number of electrical connectors required to implement all-hybrid slots in PXI-E chassis 100 may take up all available real estate on backplane 110. Under these circumstances, there may be inadequate space on backplane 110 to accommodate components such as a PCI-E switch integrated circuit (IC) implementing the PCI-E switch fabric.
One way to address the problem of inadequate space on backplane 110, as illustrated FIGS. 3 and 4, is to place certain components on another PGB in the form of a mezzanine board 305, and then connect mezzanine board 305 to backplane 110 with board-to-board connectors 310. A significant shortcoming of this approach, however, is that it requires an increase in the size of backplane 110 to accommodate the board-to-board connectors 310, which tends to decrease airflow through PXI-E chassis 100, as shown in FIG. 4. In the example of FIG. 4, the flow of air from a module in module slot 2 to an exhaust fan 410 is restricted as the edges of backplane 110 get closer to the walls of physical support structure 115. This may produce a need for higher fan speed, increasing acoustic noise, among other things.
Another way to address the problem of inadequate space on backplane 110, as illustrated by a PXI-E chassis 100′ in FIG. 5, is to remove some of module slots 1 through 18 to accommodate PCI-E switching components 505. A significant shortcoming of this approach, however, is that it decreases the available functionality of PXI-E chassis 100.
In view of at least the above shortcomings of conventional PCI-E compatible chassis, there is a general need for improved approaches to backplane design and/or placement of electrical connectors.